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<a name="hash.disable"></a><a class="link" href="disable.html" title="Disabling The Extensions">Disabling The Extensions</a>
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<p>
      While <code class="computeroutput"><a class="link" href="../boost/hash.html" title="Struct template hash">boost::hash</a></code>'s extensions are
      generally useful, you might want to turn them of in order to check that your
      code will work with other implementations of TR1. To do this define the macro
      <code class="computeroutput"><span class="identifier">BOOST_HASH_NO_EXTENSIONS</span></code>. When
      this macro is defined, only the specialisations detailed in TR1 will be declared.
      But, if you later undefine the macro and include &lt;<code class="computeroutput"><a class="link" href="reference.html#header.boost.functional.hash_hpp" title="Header &lt;boost/functional/hash.hpp&gt;">boost/functional/hash.hpp</a></code>&gt;
      then the non-specialised form will be defined - activating the extensions.
    </p>
<p>
      It is strongly recommended that you never undefine the macro - and only define
      it so that it applies to the complete translation unit, either by defining
      it at the beginning of the main source file or, preferably, by using a compiler
      switch or preference. And you really should never define it in header files.
    </p>
<p>
      If you are writing a library which has code in the header which requires the
      extensions, then the best action is to tell users not to define the macro.
      Their code won't <span class="emphasis"><em>require</em></span> the macro.
    </p>
<p>
      Translation units that are compiled with the macro defined will link with units
      that were compiled without it. This feature has been designed to avoid ODR
      violations.
    </p>
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      James<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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